Systemic Lupus (SLE) is an autoimmune disease characterized by the production of an array of anti- nuclear antibodies that affects women far more frequently than men. Abnormal B and T cell function has been extensively studied in murine models of SLE. We have developed a mouse with a deletion of Blimp-1 function uniquely in dendritic cells. Female mice develop a lupus-like serology while male mice do not. We propose to understand the alterations in dendritic cell function and the mechanism for the subsequent dysregulation of B cell function. Furthermore, we will determine why this genetic defect manifests as autoimmunity only in female mice. These studies will further our understanding of dendritic cell biology and may identify a new therapeutic target in SLE.